Exposure system, exposure method, diffractive optical element and intelligent head-mounted equipment

Abstract

The embodiment of the invention provides an exposure system, an exposure method, a diffractive optical element and intelligent head-mounted equipment. Wherein the exposure system comprises a metasurface device and an exposure substrate, the exposure substrate is located on the light emitting side of the metasurface device, and the center of the metasurface device and the center of the exposure substrate are located on the same optical axis; the metasurface device is configured to enable incident linearly polarized light LP to form right-handed circularly polarized light RCP and left-handed circularly polarized light LCP, wherein the propagation directions of the right-handed circularly polarized light RCP and the left-handed circularly polarized light LCP deflect by an angle theta relative to the optical axis; the exposure substrate is located in an overlapping area of the right-handed circularly polarized light RCP and the left-handed circularly polarized light LCP, and the right-handed circularly polarized light RCP and the left-handed circularly polarized light LCP can form an overlapped interference light field on the exposure substrate, so that the polarization holographic grating is manufactured on the exposure substrate.

Description

Technical Field

[0001] The embodiments of the present application relate to the field of optical display technology. More specifically, the embodiments of the present application relate to an exposure system, an exposure method of a polarization volume holographic grating, a diffractive optical element and an intelligent head-mounted device. Background Art

[0002] In recent years, diffractive optical elements (DOE) have been widely used in many fields due to their unique diffraction characteristics. Among them, polarization volume holographic grating (PVG) is an important diffractive optical element, and its preparation process involves cutting-edge technologies such as micro-nano processing and holographic interferometry. However, the traditional preparation method of polarization volume holographic grating has problems such as high cost and low production efficiency, especially when preparing large-area, high-precision polarization volume holographic grating, these problems are particularly prominent. Summary of the invention

[0003] The purpose of this application is to provide a new technical solution for an exposure system, an exposure method, a diffractive optical element and an intelligent head-mounted device.

[0004] In a first aspect, the present application provides an exposure system. The exposure system comprises a metasurface device and an exposure substrate, wherein the exposure substrate is located on the light-emitting side of the metasurface device, and the center of the metasurface device and the center of the exposure substrate are located on the same optical axis;

[0005] The metasurface device is configured to enable incident linearly polarized light LP to form right-handed circularly polarized light RCP and left-handed circularly polarized light LCP whose propagation directions are deflected by an angle θ relative to the optical axis;

[0006] The exposure substrate is located in the overlapping area of ​​the right circularly polarized light RCP and the left circularly polarized light LCP, and the right circularly polarized light RCP and the left circularly polarized light LCP can form a superimposed interference light field on the exposure substrate, thereby being used to produce a polarization volume holographic grating on the exposure substrate.

[0007] Optionally, a first metastructure is provided on at least a partial area of ​​the surface of the metasurface device, and the first metastructure is configured to be able to change the handedness of the circularly polarized light and control the circularly polarized light to be deflected by an angle θ relative to the optical axis and then projected onto the exposure substrate.

[0008] Optionally, the first superstructure includes a plurality of first repeated structures arranged periodically;

[0009] Each of the first repeating structures includes four first metamolecules with different rotation angles, and the four first metamolecules are arranged in sequence and spaced apart along the same direction, wherein the rotation angles of two adjacent first metamolecules differ by π / 4, and the difference in the rotation angles of the four first metamolecules can be used to change the geometric phase of the transmitted circularly polarized light, thereby achieving the change in the rotation direction of the circularly polarized light and the deflection of the transmission direction of the circularly polarized light.

[0010] Optionally, the first metastructure covers the surface of the metasurface device, and the interval between the exposure substrate and the metasurface device is D1, and 1mm≤D1≤L / 2*(1 / tanθ); wherein L is the length of the exposure substrate.

[0011] Optionally, the surface of the metasurface device further includes a second metastructure, and the second metastructure is configured to deflect the circularly polarized light by an angle θ relative to the optical axis and then project it onto the exposure substrate without changing the handedness of the circularly polarized light.

[0012] Optionally, the second superstructure includes a plurality of second repeated structures arranged periodically;

[0013] Each of the second repeating structures includes four second metamolecules with different cross-sectional sizes, and the cross-sectional sizes of the four second metamolecules show an orderly gradient along the same direction and are arranged in sequence. Through the four second metamolecules, the geometric phase of the transmitted circularly polarized light in the light transmission direction can gradually change with the changing trend of the cross-sectional size of each second metamolecule, thereby achieving the deflection of the transmission direction of the circularly polarized light.

[0014] Optionally, the surface of the metasurface device includes a first metastructure and a second metastructure arranged in parallel, and the first metastructure and the second metastructure have the same area size.

[0015] Optionally, the exposure system further comprises a phase retarder, which is arranged along the optical axis on a side of the metasurface device away from the exposure substrate, and is used to convert incident linearly polarized light LP into circularly polarized light and project it onto the first metastructure and the second metastructure, respectively.

[0016] Optionally, when the incident linearly polarized light LP passes through the phase retarder to form right-handed circularly polarized light RCP, the first metastructure can convert the right-handed circularly polarized light RCP into left-handed circularly polarized light LCP and deflect it by an angle θ relative to the optical axis before projecting it onto the exposure substrate, and the second metastructure can deflect the right-handed circularly polarized light RCP by an angle θ relative to the optical axis without changing the rotation direction before projecting it onto the exposure substrate.

[0017] Optionally, the distance between the exposure substrate and the metasurface device is D2, D2*tanθ=L / 2; wherein L is the length of the exposure substrate.

[0018] Optionally, the exposure system comprises a light source assembly, and the light source assembly is arranged along the optical axis on a side of the metasurface device away from the exposure substrate;

[0019] The light source assembly comprises a light source and a collimating and beam expanding assembly; wherein the light source is used to emit a laser beam, and the collimating and beam expanding assembly is used to collimate and expand the laser beam.

[0020] Optionally, the light source assembly further includes a linear polarizer, which is located between the light source and the collimating beam expanding assembly, and is used to convert the laser beam emitted by the light source into linearly polarized light LP.

[0021] In a second aspect, the present application provides an exposure method for a polarization volume holographic grating, the exposure method comprising:

[0022] Controlling linear polarized light to be projected onto the metasurface device;

[0023] The incident linearly polarized light is transformed into right-handed circularly polarized light RCP and left-handed circularly polarized light LCP whose propagation directions are deflected by an angle θ relative to the optical axis by the metasurface device, and projected onto the exposure substrate; wherein a photosensitive material layer is provided on the surface of the exposure substrate;

[0024] The left-handed circularly polarized light LCP and the right-handed circularly polarized light RCP form a superimposed interference light field on the photosensitive material layer, thereby forming a polarization volume holographic grating on the exposure substrate.

[0025] Optionally, the period Λx of the polarization holographic grating is: Λx=λ / 2sinθ; wherein λ is the wavelength of the incident laser beam.

[0026] In a third aspect, the present application provides a diffractive optical element, the diffractive optical element comprising:

[0027] substrate; and

[0028] The polarization volume holographic grating is formed by the exposure system according to the first aspect, and the polarization volume holographic grating is arranged on the substrate.

[0029] In a fourth aspect, the present application provides a smart head-mounted device, the smart head-mounted device comprising:

[0030] A diffractive optical element as described in the third aspect.

[0031] The beneficial effects of this application are:

[0032] The embodiment of the present application provides an exposure system for a polarization volume holographic grating. By adopting a specially designed metasurface device, efficient modulation of the incident linearly polarized light LP is achieved. The metasurface device can make the linearly polarized light form right-handed circularly polarized light RCP and left-handed circularly polarized light LCP whose propagation direction is deflected by an angle θ relative to the optical axis. This feature greatly simplifies the setting of the optical architecture of the entire optical system and reduces the sensitivity to environmental interference. At the same time, by placing the exposure substrate 5 in the overlapping area of ​​the right-handed circularly polarized light RCP and the left-handed circularly polarized light LCP, the two circularly polarized lights can form a superimposed interference light field on the exposure substrate. This interference light field is the key element necessary for making a polarization volume holographic grating, thereby achieving the purpose of efficiently and accurately making a polarization volume holographic grating on the exposure substrate.

[0033] Other features and advantages of the present specification will become apparent from the following detailed description of exemplary embodiments of the present specification with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the specification and, together with the description, serve to explain the principles of the specification.

[0035] Figure 1 One of the schematic diagrams of the working principle of the exposure system provided in the embodiment of the present application;

[0036] Figure 2 The second schematic diagram of the working principle of the exposure system provided in the embodiment of the present application;

[0037] Figure 3 The third schematic diagram of the working principle of the exposure system provided in the embodiment of the present application;

[0038] Figure 4 A schematic diagram of the structure of a metasurface device provided in an embodiment of the present application;

[0039] Figure 5 Another schematic diagram of the structure of a metasurface device provided in an embodiment of the present application;

[0040] Figure 6 The exposure system provided in the embodiment of the present application (comprising Figure 4 A schematic diagram of the structure of the metasurface device in FIG.

[0041] Figure 7 for Figure 4 A side view and a top view of the metasurface device shown in FIG.

[0042] Figure 8 for Figure 7 Schematic diagram of the first metamolecule shown in ;

[0043] Fig. 9 The exposure system provided in the embodiment of the present application (comprising Figure 5 A schematic diagram of the structure of the metasurface device in FIG.

[0044] Fig.10 for Figure 5 A side view and a top view of the metasurface device shown in FIG.

[0045] Fig.11 for Fig.10 Schematic diagram of the second metamolecule shown in FIG.

[0046] Description of reference numerals:

[0047] 1. Light source; 2. Polarizer; 3. Collimation and beam expansion assembly;

[0048] 4. Metasurface devices;

[0049] 41. The first superstructure; 411. The first repeating structure; 4111. The first supermolecule a; 4112. The first supermolecule b; 4113. The first supermolecule c; 4114. The first supermolecule d;

[0050] 42. The second superstructure; 421. The second repeating structure; 4211. The second supermolecule a; 4212. The second supermolecule b; 4213. The second supermolecule c; 4214. The second supermolecule d;

[0051] 5. Expose the substrate. DETAILED DESCRIPTION

[0052] Various exemplary embodiments of the present application will now be described in detail with reference to the accompanying drawings. It should be noted that unless otherwise specifically stated, the relative arrangement of components and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present application.

[0053] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the present application, its application, or uses.

[0054] Techniques and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the techniques and equipment should be considered part of the specification.

[0055] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0056] It should be noted that like reference numerals and letters refer to similar items in the following figures, and therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0057] The exposure system, exposure method, diffractive optical element and intelligent head-mounted device provided in the embodiments of the present application are described in detail below in conjunction with the accompanying drawings.

[0058] According to one embodiment of the present application, an exposure system is provided. Figure 1 and Figure 2 The exposure system includes a metasurface device 4 and an exposure substrate 5, wherein the exposure substrate 5 is located at the light-emitting side of the metasurface device 4, and the center of the metasurface device 4 and the center of the exposure substrate 5 are located on the same optical axis; the metasurface device 4 is configured to enable the incident linearly polarized light LP to form right-handed circularly polarized light RCP and left-handed circularly polarized light LCP whose propagation directions are deflected by an angle θ relative to the optical axis; the exposure substrate 5 is located in the overlapping area of ​​the right-handed circularly polarized light RCP and the left-handed circularly polarized light LCP, and the right-handed circularly polarized light RCP and the left-handed circularly polarized light LCP can form a superimposed interference light field on the exposure substrate 5, thereby being used to produce a polarization volume holographic grating on the exposure substrate 5.

[0059] The exposure system provided in the embodiment of the present application is newly designed for the preparation of polarization volume holographic grating (PVG). The exposure system provided in the embodiment of the present application realizes the efficient and high-precision preparation of polarization volume holographic grating through a combination of carefully designed optical elements.

[0060] In the exposure system of the embodiment of the present application, multiple optical elements are arranged along the same optical axis, which ensures the stable transmission and precise control of light, thereby improving the preparation quality of the polarization holographic grating.

[0061] The exposure system provided in the embodiment of the present application includes a metasurface device 4, which is specially designed to receive incident linearly polarized light LP. The metasurface device 4 can modulate the incident linearly polarized light LP into right-handed circularly polarized light RCP and left-handed circularly polarized light LCP whose propagation direction is deflected by an angle θ relative to the optical axis of the exposure system, see Figure 1 and Figure 2 .

[0062] The exposure system provided in the embodiment of the present application includes an exposure substrate 5, and the exposure substrate 5 is placed in the overlapping area of ​​the right-handed circularly polarized light RCP and the left-handed circularly polarized light LCP. In the overlapping area, the right-handed circularly polarized light RCP and the left-handed circularly polarized light LCP can form a superimposed interference light field. This interference light field is a key element necessary for making a polarization volume holographic grating.

[0063] The core of the exposure system of the embodiment of the present application lies in the unique design of the metasurface device 4 (Metasurface), which enables the entire exposure system to simultaneously generate left-handed circularly polarized light LCP and right-handed circularly polarized light RCP, and both beams of light are at a specific deflection angle θ with respect to the optical axis of the exposure system. This feature not only significantly simplifies the optical architecture of the exposure system, but also greatly improves the efficiency and accuracy of the preparation of polarization volume holographic gratings (PVG).

[0064] By adjusting the optical parameters (mainly microstructure parameters) of the metasurface device 4, the deflection angle θ of the left-handed circularly polarized light LCP and the right-handed circularly polarized light RCP relative to the optical axis of the exposure system can be precisely controlled, thereby achieving precise control of the optical parameters such as the final grating period.

[0065] For example, see Figure 3 The period Λx of the polarization holographic grating produced on the exposure substrate 5 is =λ / 2sinθ, wherein λ is the wavelength of the incident light.

[0066] The exposure system provided in the embodiment of the present application further includes an exposure substrate 5 located at an exposure station, and a photosensitive material layer is provided on the surface of the exposure substrate 5, for example, by coating. The left-handed circularly polarized light LCP and the right-handed circularly polarized light RCP form an interference light field on the exposure substrate 5 coated with the photosensitive material layer, and finally form a polarization volume holographic grating.

[0067] The photosensitive material layer is sensitive to the interference response of left-handed circularly polarized light and right-handed circularly polarized light, and can form the desired grating structure under the action of the interference light field. By adjusting the exposure parameters (such as exposure time, light intensity, etc.), the morphology and performance of the grating can be precisely controlled.

[0068] The exposure system provided in the embodiment of the present application adopts the metasurface device 4, which significantly simplifies the complex setting of the traditional optical architecture, and can achieve efficient polarized light modulation and interference light field formation without using multiple optical elements and complex adjustment processes. The use of the metasurface device 4 can also reduce the sensitivity of the entire exposure system to environmental interference, which enables the exposure system to maintain stable performance under various environmental conditions, thereby improving the reliability and accuracy of the exposure process.

[0069] The exposure system of the present application can efficiently and accurately produce polarization volume holographic gratings by forming a superimposed interference light field on the exposure substrate 5. This provides a new and efficient solution for the preparation of polarization volume holographic gratings, which has important application value.

[0070] In some examples of this application, see Figure 4and Figure 5 A first metastructure 41 is disposed on at least a portion of the surface of the metasurface device 4. The first metastructure 41 is configured to be able to change the handedness of the circularly polarized light and control the circularly polarized light to be deflected by an angle θ relative to the optical axis and then projected onto the exposure substrate 5.

[0071] The surface of the metasurface device 4 has a specific micro-nano structure, which can achieve light regulation. In this example of the present application, the first metastructure 41 is at least a part of the area or the entire area on the surface of the metasurface device 4.

[0072] Circularly polarized light is divided into left-handed circularly polarized light LCP and right-handed circularly polarized light RCP.

[0073] In the present application, the first metastructure 41 is configured to receive incident circularly polarized light (whether left-handed circularly polarized light LCP or right-handed circularly polarized light RCP), and change the handedness of the circularly polarized light through the design of its micro-nanostructure. For example, left-handed circularly polarized light LCP can be converted into right-handed circularly polarized light RCP, or right-handed circularly polarized light RCP can be converted into left-handed circularly polarized light LCP.

[0074] At the same time, the first metastructure 41 can also control the circularly polarized light after the rotation direction is changed to deflect by an angle θ relative to the optical axis of the exposure system. This deflection angle θ can be precisely controlled by designing the micro-nano structure of the first metastructure 41.

[0075] According to the exposure system provided by the embodiment of the present application, the circularly polarized light processed by the first metastructure 41 is projected onto the exposure substrate 5 at a specific deflection angle θ. The exposure substrate 5 is a material for recording a grating structure, and a polarization volume holographic grating can be formed thereon through the interference effect of the circularly polarized light.

[0076] In the traditional method, the preparation of polarization holographic grating requires complex optical settings, including multiple optical elements and precise optical path adjustment. However, the use of the metasurface device 4 and its first metastructure 41 in the present application can greatly simplify the optical system and reduce the number of optical elements and the complexity of the optical path.

[0077] By adjusting the micro-nano structural parameters (such as the rotation angle and size of the unit structure) of the first metastructure 41, the change in the rotation direction and the deflection angle of the circularly polarized light can be flexibly controlled. This helps to achieve precise control of the preparation process of the polarization volume holographic grating and improve the preparation accuracy and performance of the grating.

[0078] This application solves the complexity and cost problems of preparing polarization holographic gratings in traditional methods, and helps promote the application and development of polarization holographic gratings. Especially in the field of augmented reality (AR) and other fields that require high-precision gratings, the technical solution of this application has broad application prospects.

[0079] By designing the micro-nano structure of the first metastructure 41, modulation of the circularly polarized light can be achieved, including the change of the rotation direction and the control of the deflection angle. This helps to reduce the loss of light energy and improve the utilization rate of light energy. In some optimized designs, such as using a metasurface device 4 with a partitioned structure, the utilization rate of light energy can be further improved to more than 70%.

[0080] In some examples of this application, see Figure 7 The first metastructure 41 includes a plurality of first repeating structures 411 arranged periodically; each of the first repeating structures 411 includes four first metamolecules with different rotation angles, and the four first metamolecules are arranged in sequence along the same direction, wherein the rotation angles of two adjacent first metamolecules differ by π / 4, and the geometric phase of the transmitted circularly polarized light can be changed by the difference in the rotation angles of the four first metamolecules, thereby achieving the change in the rotation direction of the circularly polarized light and the deflection of the transmission direction of the circularly polarized light.

[0081] The first metastructure 41 is formed by a periodic arrangement of a plurality of first repeating structures 411. This orderly periodic arrangement is designed to effectively modulate the geometric phase of the transmitted light, thereby producing a specific and expected optical effect.

[0082] See also Figure 7 Each first repeating structure 411 includes four first metamolecules with different rotation angles, namely: first metamolecule a4111, first metamolecule b4112, first metamolecule c4113 and first metamolecule d4114; these four first metamolecules are arranged in sequence along the same direction to form a micro-nano structure with a specific rotation angle distribution.

[0083] The rotation angles of two adjacent first metamolecules differ by π / 4. The design of this rotation angle is based on the principle of geometric phase, that is, when light passes through micro-nano structures with different rotation angles, a geometric phase change related to the rotation angle will occur.

[0084] Please continue to see Figure 7 By designing the four rotation angles of the first metamolecule, for example, 0, π / 4, π / 2, and 3π / 4, respectively, the geometric phase of the transmitted circularly polarized light can be changed.

[0085] When circularly polarized light passes through the first metastructure 41, due to the difference in rotation angles between the first metamolecules, the transmitted circularly polarized light will obtain different geometric phases. This difference in geometric phase will cause the handedness of the circularly polarized light to change, for example, from left-handed circularly polarized light LCP to right-handed circularly polarized light RCP, or from right-handed circularly polarized light RCP to left-handed circularly polarized light LCP.

[0086] At the same time, due to the specific relationship between the geometric phase and the propagation direction of the light, the transmitted circularly polarized light changes its rotation direction and its transmission direction is also deflected. The deflection angle θ can be controlled by designing the micro-nanostructure parameters of the first metastructure 41 (such as the rotation angle, size, arrangement period, etc. of the first metamolecule).

[0087] By designing the rotation angle of the first metamolecule in the first metastructure 41, the geometric phase of the transmitted circularly polarized light can be changed, which helps to control the rotation direction and transmission direction of the circularly polarized light.

[0088] Since the first metastructure 41 uses a plurality of first repeating structures 411 arranged periodically, and each first repeating structure 411 includes four first metamolecules with different rotation angles, uniform modulation of incident circularly polarized light can be achieved, which helps to reduce the loss of light energy and improve the utilization rate of light energy.

[0089] In the traditional method, the preparation of polarization holographic grating requires complex optical settings and precise optical path adjustment. However, the use of the first metastructure 41 described in this example of the present application can greatly simplify the optical system and reduce the number of optical elements and the complexity of the optical path.

[0090] In addition, the change in the handedness and the deflection angle of the circularly polarized light can be controlled by adjusting the parameters such as the rotation angle, size and arrangement period of the first metamolecule in the first metastructure 41. This helps to control the preparation process of the polarization volume holographic grating and improve the preparation accuracy and performance of the grating.

[0091] For a specific example, see Figure 7 and Figure 8The first metastructure 41 includes a plurality of first repeating structures 411 arranged periodically, and the first repeating structure 411 includes four first metamolecules with different rotation angles, namely: a first metamolecule a4111, a first metamolecule b4112, a first metamolecule c4113 and a first metamolecule d4114. The four first metamolecules are arranged in sequence along the same direction, and the four first metamolecules are all nanoscale cubic structures. The rotation angles of the four first metamolecules are respectively set to 0, π / 4, π / 2, and 3π / 4, which can change the geometric phase of the transmitted circularly polarized light and deflect the circularly polarized light by an angle θ in the propagation direction.

[0092] In some examples of this application, see Figure 4 and Figure 6 , the first metastructure 41 covers the surface of the metasurface device 4, the interval between the exposure substrate 5 and the metasurface device 4 is D1, and 1mm≤D1≤L / 2*(1 / tanθ); wherein L is the length of the exposure substrate 5.

[0093] In this example of the present application, the first metastructure 41 covers the surface of the metasurface device 4, that is, only the first metastructure 41 is provided on the surface of the metasurface device 4, see Figure 4 When the metasurface device 4 is applied to the exposure system of the present application, please refer to Figure 6 The distance D1 between the exposure substrate 5 and the metasurface device 4 is designed to be controlled within the range of 1 mm to L / 2*(1 / tanθ), where L represents the length of the exposure substrate 5 .

[0094] According to this example of the present application, by placing the exposure substrate 5 close to the metasurface device 4, the propagation distance of the light during the exposure process is effectively shortened, and the diffraction and scattering of the light are significantly reduced, thereby improving the overall exposure accuracy. In addition, by controlling the distance (interval) D1 between the exposure substrate 5 and the metasurface device 4, the interference effect of the light is ensured to be optimal.

[0095] See also Figure 6 When the distance between the exposure substrate 5 and the metasurface device 4 is very small, the light energy utilization rate is relatively high. However, during the exposure process, light energy is converted into heat energy, which will cause the temperature of the metasurface device 4 and the exposure substrate 5 to rise. If the distance between the two is too close (for example, less than 1 mm), local overheating may occur, thereby affecting the performance and stability of the metasurface device 4.

[0096] In addition, when the distance between the exposure substrate 5 and the metasurface device 4 is very small (e.g., less than 1 mm), the risk of contamination and damage will also increase. For example, tiny dust particles or chemicals may adhere to the metasurface device 4, affecting its performance; at the same time, friction or collision between the exposure substrate 5 and the metasurface device 4 may also cause damage.

[0097] Although shortening the distance between the exposure substrate 5 and the metasurface device 4 can reduce the diffraction and scattering of light, in some cases, excessive proximity may induce new interference and diffraction effects, affecting the accuracy of exposure and the structural integrity of the metasurface device 4.

[0098] During the manufacturing process, it may be necessary to adjust the position of the exposure substrate 5 according to actual conditions. If the distance between the exposure substrate 5 and the metasurface device 4 is very close (for example, less than 1 mm), the difficulty of adjustment and maintenance may increase.

[0099] It can be seen that when only the first metastructure 41 is arranged on the metasurface device 4, although the exposure substrate 5 is arranged close to the metasurface device 4 to improve the utilization rate of light energy, it may also bring about problems such as increased manufacturing difficulty, thermal effect problems, pollution and damage risks, interference and diffraction effects, and difficulty in adjustment and maintenance. Therefore, in the application, it is necessary to weigh various factors and select the most appropriate distance between the exposure substrate 5 and the metasurface device 4. The more appropriate range can be 1mm to L / 2*(1 / tanθ) provided in this example of the present application.

[0100] In some examples of this application, see Figure 5 and Fig. 9 The surface of the metasurface device 4 also includes a second metastructure 42, which is configured to deflect the circularly polarized light by an angle θ relative to the optical axis and then project it onto the exposure substrate 5 without changing the handedness of the circularly polarized light.

[0101] In this example of the present application, the design of the metasurface device 4 (Metasurface) is further optimized, and its surface includes not only the first metastructure 41, but also a second metastructure 42. By arranging the first metastructure 41 and the second metastructure 42 in different areas on the metasurface device 4, light energy can be used more efficiently.

[0102] In the process of preparing polarization holographic gratings, the efficiency of light energy utilization is one of the key technical indicators. Traditional exposure schemes often have the problem of light energy waste, such as light energy not being fully projected to the target area, or being lost due to scattering, absorption, etc. during the propagation process.

[0103] In the exposure scheme of the polarization volume holographic grating of the present application, the use of a partitioned metasurface device 4 (such as the first metastructure 41 and the second metastructure 42) can significantly improve the light energy utilization rate, which can be mainly attributed to the optimization of the following aspects:

[0104] The partitioned configuration allows for more sophisticated and flexible modulation of incident light. For example, the first metastructure 41 and the second metastructure 42 can independently modulate different portions of circularly polarized light.

[0105] In the traditional exposure scheme, due to the limitation of optical elements or unreasonable optical path design, part of the light energy is not effectively utilized but is lost in space. However, through the partitioned superstructure in this example of the present application, the propagation path and deflection angle of the light can be accurately controlled, thereby ensuring that more light energy can be projected onto the exposure substrate 5 to form an interference light field.

[0106] The first metastructure 41 and the second metastructure 42 arranged in a partition on the metasurface device 4 jointly improve the light energy utilization rate. This means that under the same exposure conditions, a brighter and clearer exposure pattern can be obtained, thereby improving the efficiency and quality of preparing polarization volume holographic gratings.

[0107] In some examples of this application, see Figure 6 , Fig. 9 and Fig.10 The second metastructure 42 includes a plurality of periodically arranged second repeating structures 421; each of the second repeating structures 421 includes four second metamolecules with different cross-sectional sizes, and the cross-sectional sizes of the four second metamolecules show an orderly gradient along the same direction and are arranged in sequence. Through the four second metamolecules, the geometric phase of the transmitted circularly polarized light in the light transmission direction can gradually change with the changing trend of the cross-sectional size of each second metamolecule, thereby achieving the deflection of the transmission direction of the circularly polarized light.

[0108] See also Fig.10 The second metastructure 42 is composed of a plurality of periodically arranged second repeating structures 421; wherein each second repeating structure 421 contains four second metamolecules with different cross-sectional sizes, and the cross-sectional sizes of the four second metamolecules show an orderly gradient along the same direction and are arranged in sequence.

[0109] For example, see Fig.10 The second repeating structure 421 includes four second metamolecules, namely: second metamolecule a4211, second metamolecule b4212, second metamolecule c4213, and second metamolecule d4214. These four second metamolecules are arranged in gradually changing sizes.

[0110] When circularly polarized light passes through these second metamolecules, the phase modulation of the light is different due to the different cross-sectional sizes of each metamolecule. This phase modulation gradually changes with the change of the cross-sectional size of the metamolecule, thereby guiding the transmission direction of the circularly polarized light to deflect.

[0111] For example, the second metamolecule may be a nanocylinder, see Fig.10 and Fig.11 .

[0112] Of course, the first metamolecule and the second metamolecule may be different according to specific embodiments. The first metamolecule of volume has been described above and will not be discussed again here. For an example of the first metamolecule, please refer to Figure 7 or Fig.10 The left figure in .

[0113] The specially designed second metastructure 42 can make the transmitted circularly polarized light obtain the required phase modulation in the light transmission direction. This design avoids the problem of low light energy utilization in the traditional method (such as half of the light energy is likely to not reach the target area), thereby improving the overall light energy utilization.

[0114] The metasurface device 4 provided in the embodiment of the present application can achieve a light energy utilization rate of more than 70% based on the first metastructure 41 and the second metastructure 42 arranged in partitions.

[0115] Since the second repeating structure 421 in the second metastructure 42 is arranged periodically, the deflection angle of circularly polarized light can be flexibly controlled by adjusting the period and the cross-sectional size of the metamolecule. This flexibility gives the structure a significant advantage in preparing polarization volume holographic gratings with different deflection angle requirements.

[0116] Compared with the traditional method, the present application can use only one metasurface device 4, partition it into different metastructures, such as the first metastructure 41 and the second metastructure 42, and match it with a single exposure substrate to achieve the required phase modulation and deflection effects. This not only simplifies the preparation process, but also reduces production costs and complexity.

[0117] In some examples of this application, see Figure 5 and Fig. 9 The surface of the metasurface device 4 includes a first metastructure 41 and a second metastructure 42 arranged in parallel, and the first metastructure 41 and the second metastructure 42 have the same area size.

[0118] The surface of the metasurface device 4 is divided into two parallel regions: a first metastructure 41 and a second metastructure 42. The two regions are completely identical in area size, ensuring that they occupy equal space on the device surface.

[0119] The first metastructure 41 is responsible for modulating the incident circularly polarized light, such as right-handed circularly polarized light RCP, into left-handed circularly polarized light LCP whose propagation direction is deflected by a certain angle (e.g., angle θ); at the same time, the second metastructure 42 modulates another incident circularly polarized light, such as right-handed circularly polarized light RCP, into right-handed circularly polarized light RCP also deflected by angle θ. The two structures are arranged in parallel without interfering with each other, and can jointly form the required interference light field on the surface of the exposure substrate 5.

[0120] By arranging the first superstructure 41 and the second superstructure 42 in parallel and precisely controlling their area size and phase modulation capability, the incident light energy can be utilized to the maximum extent. This design avoids the problem of light energy waste in traditional methods, thereby improving the overall light energy utilization rate.

[0121] Compared with the traditional method, the metasurface device 4 in this example of the present application uses only one element to achieve accurate modulation and deflection of circularly polarized light, which not only simplifies the structure of the system, but also reduces the complexity and cost of the system.

[0122] Since the first metastructure 41 and the second metastructure 42 are arranged side by side on the device surface and have the same area size, the circularly polarized light generated by them can form a stable interference light field in space. This interference light field is crucial for preparing optical elements such as polarization volume holographic gratings, because it determines the period, phase distribution and final diffraction performance of the grating.

[0123] In some examples of this application, see Figure 2 The exposure system also includes a phase retarder 6, which is arranged along the optical axis on the side of the metasurface device 4 away from the exposure substrate 5, and is used to convert the incident linearly polarized light LP into circularly polarized light and project it to the first metastructure 41 and the second metastructure 42 respectively.

[0124] The phase retarder 6 is, for example, a quarter wave plate.

[0125] The exposure system provided in the embodiment of the present application, in addition to the metasurface device 4 and the exposure substrate 5, also introduces a phase retarder 6 (quarter wave plate). The phase retarder 6 is arranged on the side of the metasurface device 4 away from the exposure substrate 5 and arranged along the optical axis.

[0126] In this optical configuration, see Figure 2 , the incident linearly polarized light LP first passes through the phase retarder 6, which has specific optical properties and can convert the linearly polarized light LP into circularly polarized light. The converted circularly polarized light is then projected onto the first metastructure 41 and the second metastructure 42 on the metasurface device 4. The introduction of the phase retarder 6 makes it simple to obtain circularly polarized light that originally required complex optical settings.

[0127] After passing through the metasurface device 4, the circularly polarized light is modulated into left-handed circularly polarized light LCP and right-handed circularly polarized light RCP with specific deflection angles and rotation directions. These modulated circularly polarized lights form an interference light field in space, providing necessary conditions for the subsequent exposure process.

[0128] The introduction of the phase retarder 6 simplifies the optical architecture of the exposure system. The traditional polarization holographic grating exposure scheme often requires complex optical elements and precise optical path adjustment, but the design in this example of the present application avoids these problems.

[0129] Since the phase retarder 6 can efficiently convert linearly polarized light into circularly polarized light, the efficiency of the exposure process is improved. This means that a higher quality polarization volume holographic grating can be obtained within the same exposure time. The phase retarder 6 ensures that the circularly polarized light incident on the metasurface device 4 has a uniform polarization state and intensity distribution. This helps to form a uniformly distributed interference light field on the exposure substrate 5, thereby improving the preparation quality of the polarization volume holographic grating.

[0130] In some examples of this application, see Figure 2 and Fig. 9 After the incident linearly polarized light LP passes through the phase retarder 6 to form right-handed circularly polarized light RCP, the first metastructure 41 can transform the right-handed circularly polarized light RCP into left-handed circularly polarized light LCP and deflect it by an angle θ relative to the optical axis and then project it onto the exposure substrate 5, and the second metastructure 42 can deflect the right-handed circularly polarized light RCP by an angle θ relative to the optical axis without changing the rotation direction and then project it onto the exposure substrate 5.

[0131] See also Figure 2 The incident linearly polarized light LP first passes through the phase retarder 6 and is converted into right-handed circularly polarized light RCP, and the right-handed circularly polarized light RCP is then incident on the metasurface device 4, and the metasurface device 4 includes two independently modulated regions: a first metastructure 41 and a second metastructure 42.

[0132] Regarding the modulation of the first superstructure 41:

[0133] The first metastructure 41 has special optical properties and can receive the right-handed circularly polarized light RCP. After being modulated by the first metastructure 41, the hand direction of the right-handed circularly polarized light RCP changes and is transformed into left-handed circularly polarized light LCP; at the same time, the left-handed circularly polarized light LCP is also deflected by an angle θ relative to the optical axis and then projected onto the exposure substrate 5.

[0134] Regarding the modulation of the second superstructure 42:

[0135] Different from the first metastructure 41, the second metastructure 42 keeps the rotation direction of the right-handed circularly polarized light RCP unchanged; after being modulated by the second metastructure 42, the right-handed circularly polarized light RCP is only deflected by an angle θ relative to the optical axis of the exposure system, and then projected onto the exposure substrate 5.

[0136] About the formation of light-related fields:

[0137] On the exposure substrate 5, the left-handed circularly polarized light LCP from the first metastructure 41 and the right-handed circularly polarized light RCP from the second metastructure 42 are superimposed and interfered. This superimposed interference forms an interference light field with a specific period and phase distribution, which is the key to preparing a polarization volume holographic grating.

[0138] In this example of the present application, flexible control of the rotation direction and deflection angle of the incident circularly polarized light is achieved through independent modulation of the first metastructure 41 and the second metastructure 42.

[0139] Since the first metastructure 41 and the second metastructure 42 can modulate the incident light respectively, the light energy is effectively utilized. Compared with the traditional method, the design in this example improves the light energy utilization rate during the exposure process, thereby reducing energy consumption and cost.

[0140] The interference light field formed on the exposure substrate 5 has a uniform phase distribution and a high contrast, which helps to obtain a high-quality polarization volume holographic grating in the subsequent preparation process.

[0141] The design in this example of the present application avoids the complex optical settings and precise optical path adjustment in the traditional preparation process. Through simple optical elements and precise structural design, the preparation of high-quality polarization holographic grating can be achieved.

[0142] In some examples of this application, see Fig. 9 , the distance between the exposure substrate 5 and the metasurface device 4 is D2, D2*tanθ=L / 2; wherein L is the length of the exposure substrate 5.

[0143] According to the formula D2*tanθ=L / 2 in this example of the present application, the optimal distance D2 between the exposure substrate 5 and the metasurface device 4 can be determined. This distance D2 is one of the key factors to ensure that a complete and high-quality interference light field is formed on the exposure substrate 5.

[0144] Wherein, θ represents the deflection angle of the circularly polarized light relative to the optical axis after passing through the metasurface device 4. L is the length of the exposure substrate 5, which is one of the dimensions of the polarization volume holographic grating finally prepared. By precisely controlling θ and L, the exposure process can be controlled.

[0145] See also Fig. 9 When the linear polarized light LP is modulated by the phase retarder 6 and the metasurface device 4, left-handed circularly polarized light LCP and right-handed circularly polarized light RCP are formed, and interference occurs in space. These interference light fields form a specific light intensity distribution and phase distribution on the exposure substrate 5 at a distance D2 from the metasurface device 4. By controlling D2, it can be ensured that the interference light field is completely covered on the exposure substrate 5, thereby preparing a high-quality polarization volume holographic grating.

[0146] By accurately calculating D2, it is possible to ensure that a complete and high-quality interference light field is formed on the exposure substrate 5, which helps to obtain a polarization volume holographic grating with uniform phase distribution and high contrast in the subsequent preparation process. In addition, by controlling D2, the stability of the entire exposure system can be enhanced. In practical applications, this helps to ensure that the prepared polarization volume holographic grating has stable performance under various environmental conditions.

[0147] That is, when the metasurface device 4 adopts Figure 5 When the partition design is shown, the preferred distance between the metasurface device 4 and the exposure substrate 5 is D2*tanθ=L / 2 in this example of the present application.

[0148] In some examples of this application, see Figure 6 and Fig. 9 The exposure system includes a light source assembly, which is arranged along the optical axis on the side of the metasurface device 4 away from the exposure substrate 5; the light source assembly includes a light source 1 and a collimating and expanding assembly 3; wherein, the light source 1 is used to emit a laser beam, and the collimating and expanding assembly 3 is used to collimate and expand the laser beam.

[0149] The light source assembly is arranged along the optical axis on the side of the metasurface device 4 away from the exposure substrate 5. This arrangement ensures that the laser beam can smoothly pass through the light source assembly and the metasurface device 4, and finally form the desired interference light field on the exposure substrate 5.

[0150] The light source assembly comprises a light source 1 for emitting a laser beam. The laser beam has the characteristics of high brightness, high monochromaticity and high directivity, which make the laser beam an ideal light source for preparing a polarization holographic grating.

[0151] The light source assembly further includes a collimating and expanding assembly 3, which is used to collimate and expand the laser beam emitted by the light source 1. The collimation process ensures the directionality of the laser beam, so that the beam can propagate parallel to the optical axis. The beam expansion process increases the diameter of the laser beam, thereby increasing the coverage area of ​​the beam on the metasurface device 4, thereby improving the exposure efficiency.

[0152] The collimated and expanded laser beam is incident on the metasurface device 4. The metasurface device 4 modulates the incident laser beam to form left-handed circularly polarized light LCP and right-handed circularly polarized light RCP, and interferes on the exposure substrate 5. These interference light fields form specific light intensity distribution and phase distribution on the exposure substrate 5, thereby preparing a polarization volume holographic grating.

[0153] In some examples of this application, see Figure 6 and Fig. 9 The light source assembly further includes a linear polarizer 2, which is located between the light source 1 and the collimating beam expander assembly 3, and is used to convert the laser beam emitted by the light source 1 into linearly polarized light LP.

[0154] The polarizer 2 is located at the light-emitting side of the light source 1, and is used to convert the light beam emitted by the light source 1 into linearly polarized light LP. The introduction of the polarizer 2 ensures that the light beam subsequently entering the metasurface device 4 has a consistent polarization direction, which is important for achieving accurate exposure of the polarization volume holographic grating.

[0155] In the subsequent exposure process, the linearly polarized light LP is the basis for the modulation of the metasurface device 4. The metasurface device 4 modulates the incident linearly polarized light based on a specific optical principle (such as the PB phase principle) to form the required left-handed circularly polarized light LCP and right-handed circularly polarized light RCP.

[0156] That is, the linear polarizer 2 converts the laser beam into linearly polarized light, so that the metasurface device 4 can be modulated more effectively.

[0157] In addition, as the basis of modulation, the quality and stability of linear polarized light directly affect the formation of interference light field. The linear polarizer 2 ensures the high quality of linear polarized light LP, which helps to form a uniform and stable interference light field, thereby preparing a high-quality polarization volume holographic grating.

[0158] According to another embodiment of the present application, an exposure method for a polarization volume holographic grating is provided, and the exposure method includes the following steps S100 to S300.

[0159] Step S100 , controlling the linear polarized light to be projected onto the metasurface device 4 .

[0160] Step S100 ensures that the incident light has a consistent polarization state, providing a basis for the subsequent modulation process.

[0161] Step S200, the incident linearly polarized light is transformed into right-handed circularly polarized light RCP and left-handed circularly polarized light LCP whose propagation directions are deflected by an angle θ relative to the optical axis through the metasurface device 4, and projected onto the exposure substrate 5; wherein a photosensitive material layer is provided on the surface of the exposure substrate 5.

[0162] In step S200, the metasurface device 4 modulates the incident linearly polarized light based on a specific optical principle (such as the PB phase principle) to form the required left-handed circularly polarized light LCP and right-handed circularly polarized light RCP. These circularly polarized lights are deflected by an angle θ in space relative to the optical axis of the exposure system, ensuring that they can form a superimposed interference light field on the exposure substrate 5.

[0163] In step S300 , the left-handed circularly polarized light LCP and the right-handed circularly polarized light RCP form a superimposed interference light field on the photosensitive material layer 6 , thereby forming a polarization volume holographic grating on the exposure substrate 5 .

[0164] The exposure method provided in the embodiment of the present application uses the metasurface device 4 to precisely modulate the incident light to form high-quality left-handed circularly polarized light LCP and right-handed circularly polarized light RCP. The interference light field formed by these circularly polarized lights on the exposure substrate 5 has high precision and stability, so that high-quality polarization volume holographic gratings can be prepared.

[0165] Through the modulation of the metasurface device 4, the incident linearly polarized light LP is effectively converted into left-handed circularly polarized light LCP and right-handed circularly polarized light RCP and projected onto the exposure substrate 5. This method reduces the loss of light energy and improves the utilization rate of light energy, thereby improving the efficiency of the exposure process.

[0166] Compared with the traditional method for preparing polarization volume holographic grating, the exposure method provided by the present application reduces the complex optical settings and multiple exposure processes. It only needs to control the projection of linear polarized light LP and the modulation of SS metasurface device 4 to realize the preparation of polarization volume holographic grating. Since the method reduces the complex optical elements and multiple exposure processes, the preparation cost is reduced.

[0167] In some examples of the present application, the period Λx of the polarization holographic grating is: Λx=λ / 2sinθ; wherein λ is the wavelength of the incident laser beam.

[0168] According to the period formula of the grating described in this example of the present application, that is, Λx=λ / 2sinθ; this formula reveals the relationship between the grating period Λx, the wavelength λ of the incident light beam, and the deflection angle θ of the left-handed circularly polarized light LCP and the right-handed circularly polarized light RCP. Among them, λ is the wavelength of the incident light beam, which means that the design of the grating period is optimized based on the incident light of a specific wavelength, which is crucial to ensure the performance of the grating within a specific spectral range. 2sinθ factor, this factor reflects the influence of the light deflection angle θ on the final grating period. As θ increases, the sinθ value will also increase (in the range of 0° to 90°), thereby reducing the grating period Λx. This shows that by adjusting the angle θ, the period of the final grating can be controlled, thereby optimizing its diffraction performance.

[0169] By precisely designing the grating period Λx, the diffraction efficiency can be optimized at a specific wavelength and angle, which is crucial for achieving high-efficiency optical diffraction, interference, and holographic imaging applications.

[0170] The exposure system provided by the present application is described below through Example 1 and Example 2.

[0171] Example 1

[0172] See also Figure 6 The exposure system provided in this embodiment 1 includes a light source 1, a polarizer 2, a collimating beam expansion component 3, a metasurface device 4 and an exposure substrate 5 which are sequentially arranged along the same optical axis;

[0173] The light source 1 is a laser, which is used to project a laser beam toward the polarizer 2, and the wavelength λ of the laser beam is 441.6nm;

[0174] The polarizer 2 is used to convert the incident light into linearly polarized light;

[0175] The collimating and beam expanding component 3 is used to collimate and expand the linearly polarized light emitted by the polarizer;

[0176] The metasurface device 4 is provided with a first metastructure 41 on a surface close to the collimating beam expander 3, and the first metastructure 41 can make the incident linearly polarized light LP form right-handed circularly polarized light RCP and left-handed circularly polarized light LCP whose propagation direction is deflected by an angle θ relative to the optical axis; wherein θ is 30°;

[0177] The first superstructure 41, see Figure 7 and Figure 8, comprising a plurality of first repeating structures 411 arranged periodically; each of the first repeating structures 411 comprises four first metamolecules with different rotation angles, namely: a first metamolecule a4111, a first metamolecule b4112, a first metamolecule c4113 and a first metamolecule d4114, the four first metamolecules are arranged in sequence along the same direction, and the rotation angles of the four first metamolecules are 0, π / 4, π / 2 and 3π / 4 respectively;

[0178] The plurality of first repeating structures 411 are located on a substrate, and the substrate is, for example, TiO2 with a refractive index of 2.5;

[0179] The first metamolecule a4111, the first metamolecule b4112, the first metamolecule c4113 and the first metamolecule d4114 are all nanoscale cubes with the same size, length L=68nm, width W=172nm, height Height=600nm;

[0180] The exposure substrate 5 is located in the overlapping area of ​​the right-handed circularly polarized light RCP and the left-handed circularly polarized light LCP, and the right-handed circularly polarized light RCP and the left-handed circularly polarized light LCP can form a superimposed interference light field on the exposure substrate 5, so as to be used to produce a polarization body holographic grating on the exposure substrate 5, and the period of the polarization body holographic grating Λx=λ / 2sinθ=441.6nm; wherein, the design simulation efficiency values ​​of the right-handed circularly polarized light RCP and the left-handed circularly polarized light LCP are 41.7% and 41% respectively.

[0181] Example 2

[0182] See also Fig. 9 The exposure system of the present embodiment 2 comprises a light source 1, a polarizer 2, a collimating beam expander assembly 3, a phase retarder 6, a metasurface device 4 and an exposure substrate 5 which are sequentially arranged along the same optical axis; one difference therein is that a phase retarder 6 is introduced between the collimating beam expander assembly 3 and the metasurface device 4;

[0183] In addition, the difference between the present embodiment 2 and the above-mentioned embodiment 1 is that: the surface partition of the metasurface device 4 close to the phase retarder 6 is provided with a first metastructure 41 and a second metastructure 42, and the two metastructures are symmetrically arranged with respect to the optical axis of the exposure system, and the two metastructures modulate the incident linearly polarized light respectively to obtain left-handed circularly polarized light LCP and right-handed circularly polarized light RCP at an angle of 30° to the optical axis respectively;

[0184] The first metastructure 41 is the same as that in Example 1, and the second metastructure 42 includes a plurality of periodically arranged second repeating structures 421; the second repeating structure 421 includes four second metamolecules, namely: second metamolecule a4211, second metamolecule b4212, second metamolecule c4213, and second metamolecule d4214, and the four second metamolecules are arranged with gradually changing sizes; through the four second metamolecules, the geometric phase of the circularly polarized light transmitted in the light transmission direction can gradually change with the changing trend of the cross-sectional size of each second metamolecule, thereby achieving the deflection of the transmission direction of the circularly polarized light; the substrate of the second metastructure is also TiO2, with a refractive index of 2.5;

[0185] The cross section of the second metamolecule is circular; the diameters of the second metamolecule a4211, the second metamolecule b4212, the second metamolecule c4213, and the second metamolecule d4214 are 100 nm, 120 nm, 137 nm, and 154 nm, respectively, and the heights are all 600 nm;

[0186] The left-handed circularly polarized light LCP and the right-handed circularly polarized light RCP can form a polarization holographic grating on the exposure substrate 5 provided with the photosensitive material layer, and the period of the polarization holographic grating Λx=λ / 2sinθ=4441.6nm; wherein, the design simulation efficiency values ​​of the right-handed circularly polarized light RCP and the left-handed circularly polarized light LCP are 72.8% and 74.9% respectively.

[0187] According to another embodiment of the present application, a diffractive optical element is provided. The diffractive optical element includes a substrate and a polarization volume holographic grating formed by the exposure system as described above, wherein the polarization volume holographic grating is arranged on the substrate.

[0188] The diffractive optical element provided in the embodiment of the present application is, for example, a diffractive light waveguide, which can be used to transmit the projection light emitted by an image source (such as an optical machine) to a target position (such as a human eye) for projection imaging.

[0189] Among them, the substrate is the supporting structure of the diffractive optical element, which can ensure the stability and durability of the grating.

[0190] The diffractive optical element provided in the embodiment of the present application, the polarization volume holographic grating is formed on the substrate by using the aforementioned exposure system through precise beam modulation and interference process. The grating has PB phase modulation characteristics and can accurately control the polarization of light.

[0191] According to another embodiment of the present application, a smart head-mounted device is provided, wherein the smart head-mounted device includes the diffractive optical element as described above.

[0192] The specific implementation of the intelligent head-mounted device of the embodiment of the present application can refer to the various embodiments of the above-mentioned exposure system, so it at least has all the beneficial effects brought by the technical solutions of the above-mentioned embodiments, which will not be repeated here one by one.

[0193] The above embodiments focus on the differences between the various embodiments. As long as the different optimization features between the various embodiments are not contradictory, they can be combined to form a better embodiment. Considering the simplicity of the text, they will not be repeated here.

[0194] Although some specific embodiments of the present application have been described in detail by way of example, it should be understood by those skilled in the art that the above examples are only for illustration, not for limiting the scope of the present application. It should be understood by those skilled in the art that the above embodiments may be modified without departing from the scope and spirit of the present application. The scope of the present application is defined by the appended claims.

Claims

1. An exposure system, characterized in that: It comprises a metasurface device (4) and an exposure substrate (5), wherein the exposure substrate (5) is located on the light-emitting side of the metasurface device (4), and the center of the metasurface device (4) and the center of the exposure substrate (5) are located on the same optical axis; The metasurface device (4) is configured to enable incident linearly polarized light LP to form right-handed circularly polarized light RCP and left-handed circularly polarized light LCP whose propagation directions are deflected by an angle θ relative to the optical axis; The exposure substrate (5) is located in the overlapping area of ​​the right-handed circularly polarized light RCP and the left-handed circularly polarized light LCP, and the right-handed circularly polarized light RCP and the left-handed circularly polarized light LCP can form a superimposed interference light field on the exposure substrate (5), thereby being used to produce a polarization body holographic grating on the exposure substrate (5).

2. The exposure system according to claim 1, characterized in that: A first metastructure (41) is provided on at least a portion of the surface of the metasurface device (4), wherein the first metastructure (41) is configured to be able to change the handedness of circularly polarized light and control the circularly polarized light to be deflected by an angle θ relative to the optical axis and then projected onto the exposure substrate (5).

3. The exposure system according to claim 2, characterized in that: The first superstructure (41) includes a plurality of first repeated structures (411) arranged periodically; Each of the first repeating structures (411) includes four first meta-molecules with different rotation angles, and the four first meta-molecules are arranged in sequence along the same direction, wherein the rotation angles of two adjacent first meta-molecules differ by π / 4. By means of the difference in the rotation angles of the four first meta-molecules, the geometric phase of the transmitted circularly polarized light can be changed, thereby achieving the change in the rotation direction of the circularly polarized light and the deflection of the transmission direction of the circularly polarized light.

4. The exposure system according to claim 2 or 3, characterized in that: The first metastructure (41) covers the surface of the metasurface device (4), the interval between the exposure substrate (5) and the metasurface device (4) is D1, and 1mm≤D1≤L / 2*(1 / tanθ); wherein L is the length of the exposure substrate (5).

5. The exposure system according to claim 2, characterized in that: The surface of the metasurface device (4) further comprises a second metastructure (42), wherein the second metastructure (42) is configured to deflect the circularly polarized light by an angle θ relative to the optical axis and then project the circularly polarized light onto the exposure substrate (5) without changing the handedness of the circularly polarized light.

6. The exposure system according to claim 5, characterized in that: The second superstructure (42) includes a plurality of second repeated structures (421) arranged periodically; Each of the second repeating structures (421) includes four second meta-molecules with different cross-sectional sizes, and the cross-sectional sizes of the four second meta-molecules show an orderly gradient along the same direction and are arranged in sequence. Through the four second meta-molecules, the geometric phase of the circularly polarized light transmitted in the light transmission direction can gradually change with the change trend of the cross-sectional size of each second meta-molecule, thereby achieving the deflection of the transmission direction of the circularly polarized light.

7. The exposure system according to claim 6, characterized in that: The surface of the metasurface device (4) comprises a first metastructure (41) and a second metastructure (42) arranged in parallel, and the first metastructure (41) and the second metastructure (42) have the same area size.

8. The exposure system according to claim 6, characterized in that: The exposure system further comprises a phase retarder (6), wherein the phase retarder (6) is arranged along the optical axis on a side of the metasurface device (4) away from the exposure substrate (5), and the phase retarder (6) is used to convert incident linearly polarized light LP into circularly polarized light and project the circularly polarized light onto the first metastructure (41) and the second metastructure (42), respectively.

9. The exposure system according to claim 8, characterized in that: When the incident linearly polarized light LP passes through the phase retarder (6) to form right-handed circularly polarized light RCP, the first metastructure (41) can transform the right-handed circularly polarized light RCP into left-handed circularly polarized light LCP and deflect the light by an angle θ relative to the optical axis before projecting it onto the exposure substrate (5), and the second metastructure (42) can deflect the right-handed circularly polarized light RCP by an angle θ relative to the optical axis without changing the rotation direction before projecting it onto the exposure substrate (5).

10. The exposure system according to claim 7, characterized in that: The distance between the exposure substrate (5) and the metasurface device (4) is D2, D2*tanθ=L / 2; wherein L is the length of the exposure substrate (5).

11. The exposure system according to claim 1, characterized in that: The exposure system comprises a light source assembly, wherein the light source assembly is arranged along the optical axis on a side of the metasurface device (4) away from the exposure substrate (5); The light source assembly comprises a light source (1) and a collimating and beam expanding assembly (3); wherein the light source (1) is used to emit a laser beam, and the collimating and beam expanding assembly (3) is used to collimate and expand the laser beam.

12. The exposure system according to claim 11, characterized in that: The light source assembly further comprises a linear polarizer (2), wherein the linear polarizer (2) is located between the light source (1) and the collimating beam expansion assembly (3), and the linear polarizer (2) is used to convert the laser beam emitted by the light source (1) into linearly polarized light LP.

13. A method for exposing a polarization holographic grating, characterized in that: include: Controlling linearly polarized light to be projected onto the metasurface device (4); The incident linearly polarized light is transformed into right-handed circularly polarized light RCP and left-handed circularly polarized light LCP whose propagation directions are deflected by an angle θ relative to the optical axis by the metasurface device (4), and projected onto the exposure substrate (5); wherein a photosensitive material layer is provided on the surface of the exposure substrate (5); The left-handed circularly polarized light LCP and the right-handed circularly polarized light RCP form a superimposed interference light field on the photosensitive material layer (6), thereby forming a polarization volume holographic grating on the exposure substrate (5).

14. The exposure method according to claim 13, characterized in that: The period Λx of the polarization holographic grating is: Λx=λ / 2sinθ; wherein λ is the wavelength of the incident laser beam.

15. A diffractive optical element, characterized in that: include: substrate; and The polarization volume holographic grating formed by the exposure system according to any one of claims 1 to 12 is arranged on the substrate.

16. A smart head mounted device, characterized in that: include: A diffractive optical element as claimed in claim 15.

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